Piezoelectric oscillator or vibrator for ultrasonic waves, especially as an instrument for therapeutical treatment and diagnosis



Dec. 27. 1995 R. POHLMAN 2,728,869

PIEZOELECTRIC OSCILLATOR OR VIBRATOR FOR ULTRASONIC WAVES, ESPECIALLY AS AN INSTRUMENT FOR THERAPEUTICAL TREATMENT AND DIAGNOSIS Filed Jan. 6, 1950 2 Sheets-Sheet 1 1 5- z 4 I I 4 C; ny

INVENTOR REIMAR F'DHLMAN Dec. 27. 1905 o MAN 2,728,869

PIEZOELEICT OSCILLATOR VIBRATOR FOR ULTRASONIC WAVE ESPECI LY AN L RUMENT FOR THERAPEUTICA REA ENT A DIAGNOSIS Filed Jan. 6, 1950 2 Sheets-Sheet 2.

V WWW INVENTOR REIMAR F'IJHLMAN AEIENT United States Patent PIEZOELECTRIC OSCILLATOR OR VIBRATOR FOR ULTRASONIC WAVES, ESPECIALLY AS AN IN- STRUMENT FOR THERAPEUTICAL TREAT- MENT AND DIAGNOSIS Reimar Pohlman, Zurich, Switzerland, assignor to USAG Ultraschall A. G., Zurich, Switzerland, a company of Switzerland Application January 6, 1950, Serial No. 137,092

3 Claims. (Cl. 3108.7)

This invention relates to a piezoelectric oscillator or vibrator for ultrasonic waves that is utilizable in particular as an instrumentfor purposes of therapeutic treatment (so-called massage-head). An object of the present invention is the provision of an instrument which is distinguished by a compact design that enables a particularly high intensity of output to be radiated, and not only ensures, even when high voltages are used, perfect electrical protection of the body of the patient under treatment and painless transmission of the ultrasonic vibrations to said patient, but also conducts away and otherwise diminishes, in an eflicient manner, the heat generated in the oscillatory system. These advantages are primarily achieved according to the invention by disposing on that side of the vibrator from which the ultrasonic waves are emitted a metal plate the thickness of which is an integral multiple of half the ultrasonic wavelength (M2) and conveniently double said half wave-length (i. e., A). The result of this arrangement is that the surface of contact between the vibrator and the metal exactly coincides with the nodal pressure point, i. e., in the loop of the ultrasonic Waves, so that said surface of contact is mechanically relieved.

In accordance with a preferred embodiment of the invention, said metal plate is firmly joined mechanically to the vibrator proper, for instance a piezoelectric resonator, by cementing with a solvent-free cement. Particularly advantageous for use as the cement for this purpose is a polymerization cement whose state of aggregation at operating temperatures is that of a solid. Instead of the polymerization cement it is also possible to use a thin film of oil or a thin film of a suitable grease or Canada balsam or the like, by means of which the piezoelectric resonator is mechanically joined to the metal plate in the known manner, but this joint is sufliciently firm only if the two elements to be joined together are each individually tuned to the same natural frequency.

The invention will appear more clearly from the following detailed description when taken in connection with the accompanying drawings, showing by way of example, preferred embodiments of the inventive idea. In the drawings:

Figures 1 to 7 are diagrams each of which illustrates a separate embodiment of the inventive idea.

In order to enable the quartz to operate against a layer of low characteristic impedance, thereby securing improved adaptation of the oscillator to the highfrequency generator, it may be found expedient to dispose between the quartz and the metal plate an appropriately tuned layer of a medium of low characteristic impedance and high tensile strength such as unvulcanized rubber, etc. The characteristic impedance of the cemented-on plate may also be reduced by providing said plate at the cemented joint with recesses 10 so adapted in depth and cross-section that on the one hand good transmission of sound from the quartz 2d to the plate 1d is achieved (Fig. and on the other 2,728,869 Patented Dec. 27, 1955 the Fresnel lens, an influencing of the radiation field in the desired manner is achieved.

In order to prevent a portion of the ultrasonic output being radiated otf in the rearward direction, i. e., by the back electrode located on the rear side of the piezoelectric resonator, a metal mass 3 or some other,

for instance ceramic, superficially metallized mass (as shown in Figs. 1 and 5) out of tune with the oscillating system is used as the back electrode in accordance with a further embodiment of the invention, which mass, whilst standing in excellent electrical contact with the oscillating system, is at the same time arranged in such slight mechanical contact therewith that no or practically no energy is withdrawn from the oscillating system thereby. Conveniently used as such a back electrode is a metal plate which, on its surface facing the piezoelectric resonator, is either well roughened or sand blasted or provided with mechanically-produced grooves or the like. In this way it is possible to ensure that the contact between the metal plate serving as the back electrode and the, conveniently, metallized surface of the piezoelectric resonator is punctual or linear only, so that the greater portion of the surface of the back electrode remains out of mechanical contact with the piezoelectric resonator without, however, satisfactory electrical contact between the two parts suffering thereby. According to still another embodiment of the oscillator, in cases where the vibrator consists of a plurality of separate pieces of quartz (2'a 2"a) (as shown by Fig. 2) (a so-called mosaic quartz), the back electrode may consist of a flexible metallic mass 4, e. g. a copper-wire net, pressed against the vibrator by an elastic cushion or pad 5.

In order to prevent, in cases where a metal plate is used as the back electrode, undesirable corona discharges from arising on said back electrode, it is advisable so to arrange the layout that the metal plate projects slightly beyond the edge of the piezoelectric resonator and is well rounded on all sides, as shown in Figs. 1 and 2. This arrangement at the same time affords the further advantage that it is possible to operate the oscillator, without hesitation, under relatively very high voltage, this being, as is known, important if it is desired to achieve a particularly high density of output. For, as a result of the use of the design here selected, sparkovers, which would result in the formation of a luminous arc dangerous to the piezoelectric resonator, are avoided.

It is particularly convenient in this connection to make the electrode of such thickness, or at least to make the edge of the electrode of such width, that as homogeneous as possible a cylindrical field arises between the electrode and the grounded outer jacket.

A further protection against such undesirable sparkovers is achieved, as shown in Fig. 4, by providing a length of cylindrical or tapering metal tube 6 coaxial with the piezoelectric resonator, said tube surrounding the piezoelectric resonator and the back electrode whilst being suitably spaced therefrom. The end achieved by the provision of this length of tube is that, in a manner In this position, however, the are no longer constitutes a danger to the quartz and does not in any way jeopardize the useful life of the object of the invention.

The oscillatory system operates at maximum efficiency when not only any radiation of its ultrasonic output in a rearward direction, i. e., by the back electrode, is prevented as far as possible, but, in addition, if also the diameter of the vibrator plate is tuned to the corresponding natural radial frequency. In addition it is desirable to choke as far as possible any radial deflection of the generated vibrations in the direction of the handle. According to a further embodiment of the invention, this aim is achieved by providing in the metal plate located on the radiating side of the piezoelectric resonator one or a plurality of annular grooves 4c whose diameter and depth are selected in accordance with the purpose stated.

In order by special means to render ineffective as far as possible the waste heat inevitably generated in the oscillator in accordance with the invention, and to deflect said waste heat from the closure plate itself, it is possible, in accordance with a further embodiment of the invention, to provide a special filling mass 9 (as shown in Fig. 3) behind the metallic mass, for instance a metal plate, serving as the back electrode, said filling mass being, for electrical reasons, preferably not in direct contact with said metallic mass, through which filling mass 9 the thermal capacity of the structural members of the oscillator is enhanced. A filling mass arranged in this way is particularly effective if its melting-point or point of transformation is in the vicinity of the maximum desired operating temperature and if it at the same time possesses as high as possible a heat of fusion or of transformation. In the case of ultrasonic oscillators used for therapeutic purposes (electric vibrators for massage) it is expedient to employ a filling mass whose melting or transformation point is as near as possible to 37 C., as this is the temperature found most agreeable when physical contact with the instrument takes place. Examples of substances that can be used to constitute such a mass are phenol, lauric acid, capric acid, p-toluidin and similar organic compounds, and also low-melting metallic alloys, or such inorganic salts as sodium thiosulphate; tetracresyl silicate, for instance, and many other substances, can be used as a mass of high thermal capacity.

In stationary treatmen of the human body with ultrasonics, it is often found n cessary to allow the radiation to take effect from several directions 'or over large surfaces, even on pronouncedly curved areas of the body. This can be done by the simultaneous use of a plurality of separate oscillators pressed against the appropriate areas of the body by springs or similar elastic devices or by means of a suitable stand. For the stationary irradiation of pronouncedly curved areas of the body it is proposed in accordance with the invention that an elastically deformable vibrator surface be used comprising a multiplicity of flat-built oscillators, comprising metal plates 1e and resonators 2e of Fig. 6, or metal plates 1] and resonators 2f of Fig. 7 held together by elastic members, springs, rubber, etc., such as indicated by members 18 of Figs. 6 and 7, respectively, flexibly coupling the metal plates 12 or If, respectively. As is appropriate to the widely-varying indications, it is advisable so to adapt the surface of the vibrator that the individual vibrators can, as shown in Fig. 6, be assembled to form a long row, a square, etc., etc. The individual vibrators are in this case independent radiators surrounded by an insulating casing 12 and jointly pressed, by an elastic medium such as a sponge-rubber pad 13, against the area of the body to be treated. It is also possible, for the purposes of such treatment, to press against the appropriate areas of the body an ultrasonic pad or cushion of predetermined form similar to a heating pad, in which cushion the individual vibrators are non-interchangeably interconnected by elastic means, and a common back electrode in the form of a flexible metallic net 4f, which is pressed up by a pad orcushion 5 of a material of low loss-angle (Fig. 7). The whole is covered with a flexible envelope 12. For the purpose of pressing on this sound pad, metal plates of predetermined curvature may be used, said curvature either coinciding with the curvature of the bodily area to be treated or providing the desired focusing of the radiators in this way arranged to radiate convergently. Should it be desired to achieve these effects with a single plate, it is advisable to make the latter of lead. It is also possible to assemble the individual radiators permanently for special, frequentlyrepeated cases such as nasal treatment, treatment of the knee, etc. These devices, and the sound cushions or pads referred to, are secured to the appropriate areas of the body, during treatment, by means of elastic members, springs, elastic bands, etc., or pressed against said areas by a flexibly-operating stand.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is:

1. In combination, a plurality of piezoelectric resonators, a plurality of metal plates each associated with one of said resonators and firmly connected to one side thereof, means for flexibly connecting said metal plates in juxtaposition to form a flexible mosaic-like surface adapted to transmit ultrasonic waves, electricallyintegral flexible back-electrode means in electrical contact with said resonators on the side thereof remote from said metal plates, and a flexible mat of electrically-insulating material disposed on the side of said backelectrode means remote from said resonators, said combination being adapted, under pressure against said mat, to establish contact between said mosaic-like surface and a curved surface for transmitting said ultrasonic waves thereto.

2. In combination, a plurality of piezoelectric resonators, a plurality of meta] plates each associated with one of said resonators and firmly connected to one side thereof, means for flexibly connecting said metal plates in juxtaposition to form a flexible mosaic-like surface adapted to transmit ultrasonic waves, electrically-integral flexible back-electrode means in electrical contact with said resonators on the side thereof remote from said metal plates, a flexible mat of electrically-insulating spongy material disposed on the side of said back-electrode means remote from said resonators, and a flexible cover of electrically-insulating material covering the side of said mat remote from said electrode means, said combination being adapted, under pressure against said cover, to establish contact between said mosaic-like surface and a curved surface for transmitting said ultra sonic waves thereto.

3. In combination, a plurality of piezoelectric resonators, a plurality of metal plates each associated with one of said resonators and firmly connected to one side thereof, means for flexibly connecting said metal plates in juxtaposition to form a flexibly mosaic-like surface adapted to transmit ultrasonic waves, electrically-integral flexible back-electrode means in electrical contact with said resonators on the side thereof remote from said metal plates, a plurality of electrically-insulating covers each associated with one of said resonators and covering the side of said back-electrode means remote from said resonators, and a flexible mat of electricallyinsulating material disposed on the side of said electrode means remote from said resonators, said combination being adapted, under pressure against said mat, to establish contact between said mosaic-like surface and a curved surface for transmitting said ultrasonic waves thereto.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Steinberger Dec. 15, 1936 Sawyer Jan. 11, 1938 Pohlman May 19, 1942 Gruetzmacher June 29, 1943 Hayes Apr. 24, 1945 Beniofi Aug. 6, 1946 Shapiro Oct. 8, 1946 10 Mason Feb. 25, 1947 Washburn Sept. 23, 1947 6 Franklin Aug. 17, 1948 Smoluchowski Jan. 25, 1949 Jaffee Feb. 14, 1950 Holden Feb. 28, 1950 Roberts Mar. 13, 1951 Chess Aug. 14, 1951 Keller Feb. 26, 1952 FOREIGN PATENTS France May 21, 1927 Italy Mar. 3, 1945 

